This research project will systematically examine the effect of plasma renin activity, ACTH, potassium, and sodium upon plasma aldosterone concentrations in normal subjects and five selected groups of hypertensive patients. Each particular group has a distinct and different abnormality associated with aldosterone production. An analysis of the interactions of the various aldosterone stimuli will provide important information on aldosterone physiology in hypertensive patients and in normal subjects. Multiple hormonal assays will be performed during various maneuvers designed to alter a single stimulus while maintaining the others under standardized conditions. These include evaluation of circadian rhythms in recumbent subjects, oral and intravenous sodium loading, suppression of ACTH with glucocorticoids, and infusion of graded concentrations of ACTH and angiotensin II. A fifth and as yet unidentified stimulus for aldosterone has been postulated. An in vitro perfusion system using the aldosterone response of isolated adrenal cells to a stimulus will be used as a bioassay for this hormone. If its presence is confirmed, biochemical characterization will be attempted.